These days, automobiles tend to have an, increased vibration of engine roll in case of engine starting, abrupt starting and braking of an automobile, or gear shifting, due to increased output of power from the engine.
Further, while driving, depending on road conditions, an exhaust pipe is vibrated.
The exhaust pipe is connected to an engine of an automobile to discharge the exhaust gas, and in an intermediate part between the engine and the exhaust pipe, a flexible tube is provided as a decoupler joint, which is firm and compact enough to absorb and buffer displacements of vibration, load of impact, heat distortion, etc.
As shown in FIG. 1 and disclosed in EP 0410089 A1, a conventional flexible tube includes a bellows member (10) made of metallic material in the form of a corrugated cylinder to absorb stresses due to expansion, contraction or bending thereof, and an interlock member (53) provided inside of the bellows member (10) to absorb stresses due to expansion, contraction, bending, etc. and controlled to be displaced within the limit of elasticity of the bellows member (10), so that the exhaust gas can flow therethrough smoothly and the bellows member (10) can be protected from the exhaust gas in high temperatures.
The conventional flexible tube further includes outer braids (20) enclosing the external surface of the bellows member (10).
With the outer braids (20) surrounding the bellows member (10), both ends of the outer braids (20) are circumferentially compressed with fixing caps (30) and they are spot-welded together for secure attachment.
With the above structure, the conventional flexible tube is connected to the engine at one end and to the exhaust pipe at the other end, thus facilitating the smooth passage of the exhaust gas therethrough and absorbing the impact and stresses generated between the engine and the exhaust pipe through the expansion and contraction of the bellows member (10) and the interlock member (53).
The conventional flexible tube, however, has been designed to be long in its total length to improve the riding comfort of drivers and passengers of the automobile, and accordingly the bellows member (10) was corrugated long enough to have many ridges and furrows.
Accordingly, when over-vibration occurred in the exhaust system, the vibration on the flexible tube increased, in which case the outer braids (20) came into contact with the bellows member (10) intermittently and such contact caused abrasion and noise. Thus, N.V.H. (noise, vibration & harshness) evaluation deteriorated and the durability of the flexible tube became reduced.
In order to solve these problems, the inventor has proposed a flexible tube for an exhaust pipe of an automobile in Korean Patent Application No. 2004-56469.
The proposed flexible tube comprises, as shown in FIG. 2, a bellows member (10) formed in the shape of a hollow cylinder having a predetermined width and length and corrugated to have alternate ridges (11) and furrows (12) along its outer periphery; outer braids (20) woven at predetermined angles and provided at a predetermined distance from the outer periphery of the bellows member (10) to enclose the bellows member (10); fixing caps (30) fitted onto both side ends of the outer braids (20) respectively, so that both side ends of the outer braids (20) can be fixed around both side ends of the bellows member (10); and a spring member (40) having elasticity and provided on a circumferential surface of the outer braids (20) to be closely contacted thereto, whereby the spring member (40) absorbs the over-vibration generated in the exhaust system and promotes the damping effect of the outer braids (30) and the bellows member (10), and thus it cannot only absorb the over-vibration generated in the exhaust system, but also restrain the subsequent amplified over-vibration in the flexible tube.
However, in the above conventional flexible tube, since the bellows member (10) was formed to have no ridges and furrows at a part where the spring member (40) was provided, the vibration generated from the flexible tube itself could be controlled, but the expansion and contraction of the bellows member (10) was not enough to control the vibration and exhaust noise generated while driving.
Further, with the above structure of the conventional flexible tube, since the vibration to be absorbed by the bellows member (10) could not be distributed uniformly but partly concentrated over the bellows member (10), durability of the bellows member (10) remarkably deteriorated.
In addition, the flexible tube was usually constructed in a manner that the impact and vibration generated at both side ends thereof should be transmitted to its central part. However, since the ridges and furrows of the bellows member (10) were not provided partly, the impact and vibration could not be effectively absorbed in the central part of the bellows member (10).